A write-back method has been known as a method of writing data using a cache. For example, in a case in which write to a storage device is controlled through the write-back method, a control device responds to a host at a point in time at which write data transmitted from the host is written to a cache. The control device writes the write data store in the cache to the storage device at a timing which is not synchronized with the write to the cache, for example, during a spare time in a subsequent process.
A write-through method has been known as another method of writing data using a cache. For example, in a case in which the write to the storage device is controlled through the write-through method, the control device responds to the host after the write data transmitted from the host is written in the cache and the storage device. As described above, in the write-through method, the write to the storage device occurs before the control device responds to the host, and thus the performance of an access process is deteriorated compared to the write-back method.
As an example of a technology related to a cache, a technology as follows has been proposed. In the technology, in a case in which a problem has occurred in a second cache memory to which data stored in a first cache memory is mirrored, the data is mirrored to a third cache memory in which a problem has not occurred.
In addition, as an example of another technology related to a cache, a storage system has been proposed in which a plurality of control devices each include a local cache and a mirror cache, and the local cache of a certain control device is duplicated with the mirror cache of an adjacent control device, thereby cyclically duplicating the caches.
Related techniques are disclosed in, for example, Japanese Laid-open Patent Publication No. 2005-43930 and International Patent Pamphlet No. WO 2004/114115.